It was not clear who carried out the airstrikes. Misrata militia leaders have blamed past attacks on forces allied to renegade Gen. Khalifa Hifter, who has been leading a campaign against Islamic extremists in the country’s east and has used helicopters. But there is little evidence that he has the capability to carry out such strikes from hundreds of miles away and with what appear to be guided munitions.

The mysterious airstrikes have fuelled speculation that foreign powers are covertly intervening in Libya’s militia violence. Neighbouring Algeria, Italy and other countries have denied involvement. Libya’s government has called on the military to investigate.

The militia leader said the warplanes targeted the Interior Ministry and several militia positions, setting fire to a warehouse. He said two sons of the head of the military council of Misrata militias, Ibrahim Bin Rajab, were among the wounded. He spoke on condition of anonymity as he wasn’t authorized to speak to journalists.

Mohammed al-Gharyani, the militia spokesman, said more than 30 fighters were wounded in the airstrikes, but that the militia had not abandoned its positions, including the Interior Ministry, the army headquarters and the military police headquarters.

Al-Gharyani said militia fighters from other areas and towns were joining the Misrata forces and “our response will be severe.”

Libya is witnessing its worst spasm of violence since Moammar Gadhafi was toppled in 2011. Many of the rebel brigades, which helped overthrow the longtime dictator, have become powerful, heavily armed militias.

A battle for control of Tripoli’s international airport and surrounding areas has been raging for weeks, pitting the powerful Zintan militia from the western mountains against the Islamist-allied Misrata militia, named for the coastal city where it waged some of the most intense battles of the uprising.